LONG-TERM EFFECTS OF REPEATED ELECTROCONVULSIVE SHOCK ON EXPLORATORY-BEHAVIOR AND SEIZURE SUSCEPTIBILITY TO LIDOCAINE IN RATS

Electroconvulsive shock (ECS) has anticonvulsant properties while a pr oconvulsant effect has not, so far, been documented. In the present ex periments, we determine whether repeated ECSs lead to an increased sei zure susceptibility to lidocaine (lignocaine) in rats. Furthermore, we investigated whether ECS will cause prolonged changes in the locomoti on and exploratory activity of the animals. Two groups of rats receive d 18 ECSs: the first group (ECS-WEEKLY) was given ECS once a week, the second (ECS-DAILY) once a day. A third group (ECS-SHAM) received only sham ECS. Five, as well as 10 weeks after the last ECS, the ECS-WEEKL Y group made significantly fewer ''hole visits'' in an eight hole box than did the ECS-SHAM group. The ECS-DAILY group also made fewer hole visits than the ECS-SHAM group, but the difference was only significan t ten weeks after the last ECS. No significant difference in locomotor activity was found. Twelve weeks after the last ECS, all rats receive d an injection of a high dose of lidocaine (65 mg/kg i.p.). ECS was ob served to have a significant effect on the number of animals convulsin g in response to the lidocaine challenge. Sixty percent (6/10) of the animals in the ECS-WEEKLY group and 20% (2/10) of those in the ECS-DAI LY group convulsed, whereas none of the animals (0/12) in the ECS-SHAM group had convulsions. Thus, the present study shows that ECS may ind uce prolonged changes in the exploratory behaviour of rats and in thei r sensitivity to the convulsant effects of lidocaine.